The present invention relates to a trimmer capacitor having a ceramic dielectric member.
Generally, trimmer capacitors using ceramic as a dielectric member have a stator electrode, a ceramic dielectric member and a rotor electrode carried on an insulating substrate formed, for example, from a plastics material. The rotor electrode and the ceramic dielectric member are typically attached to a rotor shaft rotatably inserted into the stator electrode and the insulating substrate. The rotor shaft may be rotated to change the confronting area between the rotor electrode and the stator electrode, and the capacitance value may thus be changed.
In a trimmer capacitor of such type, the ceramic dielectric member typically includes titanium dioxide (TiO.sub.2) as a main ingredient, and thus has a specific inductive capacitance of 10 to 100 times as large as a general ceramic or plastic film. In addition, a ceramic material having titanium dioxide has excellent electric characteristics such as a good high frequency characteristic. However, such a ceramic dielectric member has poor mechanical elasticity and is very fragile. In the case of a ceramic member made highly dielectric, barium titanate is often used and this causes an increase in the mechanical defects, and the capacitor becomes sensitive to slight mechanical and external factors. The capacitance value set in such capacitors and their electric characteristics thus become unstable with disadvantage.
Therefore, an object of the present invention is to provide a trimmer capacitor of such structure that the mechanical strength of the ceramic dielectric member is increased.
Other object of the present invention is to provide a trimmer capacitor in which the thickness of the ceramic dielectric member can be reduced, to thereby obtain high capacitance values.
A further object of the present invention is to provide a trimmer capacitor having a wide range of capacitance values.
These objects are met by forming the stator electrode directly on the dielectric member and soldering a terminal to the stator electrode. The dielectric member thus need not be rotated and can have its mechanical strength enhanced by the stator electrode and terminal.
Other objects, advantages and features of the present invention will be more apparent from the illustration of the drawing and the description of the embodiment of the present invention.